Foam prevention in extractive stripping of sulfolane solvent extract

ABSTRACT

GASOLINE BOILING RANGE AROMATICS ARE RECOVERED FROM A SULFOLANE EXTRACT CONTAINING SULFOLANE, GASOLINE BOILING RANGE AROMATICS, AND MINOR AMOUNTS OF LIGHT PARAFFINS BY EXTRACTIVE STRIPPING IN THE PRESENCE OF ADDED HEAVY PARAFFINIC HYDROCARBON TO REMOVE THE LIGHT PARAFFINS AND FRACTIONATION TO SEPARATE THE AROMATICS AND SULFOLANE.

May 9, 1972 F. J. ZUIDERWEG ETAL 3,661,773

["(JM I'A'IA'JVJNTION 1N EXTHACTIVE STRIPPING OF SULFOLANE SOLVENT EXTRACT Filed oct. a, 1969 AROMATICS HEAVY PARAFFIN INVENTORS:

FREDER IK J. ZUIDERWEG HENDRIK J- SCHEFFER THEIR ATTORNEY v 3,661,773 Patented May`9, 1972 United States Patent "Office U.S. Cl. 208-321 5 Claims v ABSTRACT 0F THE DISCLOSURE Gasol-ine boiling range aromatics are recovered from a Sulfolane extract containing Sulfolane, gasoline boiling range aromatics, and minor amounts of light parains by extractive stripping in the presence of yadded heavy parainic hydrocarbon to remove the light parafns vand fractionation to separate the aromatics and Sulfolane.

BACKGROUND OF THE INVENTION This invention relates to an improved process for separating and recovering aromatics from mixtures of gasoline boiling range hydrocarbons by extraction with Sulfolane. More particularly it relates to the recovery of aromatics from a Sulfolane extract.

It is Well known that when mixtures of aromatic and nou-aromatic 4hydrocarbons are contacted with Sulfolane the aromatic hydrocarbons preferentially dissolve in the Sulfolane. Liquid/liquid extraction processes employing this principle have been developed for isolation of aromatics. In these processes it is possible to select extraction conditions to effect a Very efficient removal of aromatics into the Sulfolane extracting liquid. Unfortunately, at such conditions Sulfolane also dissolves minor but significant amounts of light paraflins. When the aromatics are later recovered from the Sulfolane extract, for example by distillation, they contain these light parains which are deleterious to the aromatic quality.

One solution to this problem is to remove these light paraffins from the Sulfolane extract by taking them overhead in an extractive stripper before recovery of the aromatics from the extract. However, foaming problems are often encountered in such extractive stripping. This foaming seriously limits stripper eiciency. Addition of conventional anti-foam agents such as silicones, alcohols, and the like is unattractive as large amounts of these relatively expensive materials must be used, and they may also contaminate the recovered hydrocarbon products.

STATEMENT OF THE INVENTION It has now been found that aromatics can be recovered with improved eciency from a Sulfolane extract which contains Sulfolane, aromatics and minor amounts of closely boiling light para'ins by rst extractively stripping the extract in the presence of minor amounts of added heavy parafnic hydrocarbons to remove residual light parailins and then fractionating the resulting stripped extract to remove the aromatics as a distillate fraction and to isolate the Sulfolane and added heavy paraffmic hydrocarbons as a second bottoms. Very small amounts, generally not more than 100 p.p.m. by weight, of heavy paranic hydrocarbons need be added. When Sulfolanecontaining fractionation bottoms are not recycled, there is no product contamination problem. If the bottoms are recycled, small amounts of the heavy paraffin may appear in the non-aromatic rainate, but if desired it can be removed by distillation. For this reason its initial boiling point is desirably at least about C. higher than the end boiling point of the non-aromatics in the mixture. This invention is very suitably employed in processes for the separation of aromatics from mixtures of gasoline boiling range hydrocarbons. l

In the following description of the invention reference will be made to the accompanying drawing wherein the single figure represents, more or less diagrammatically, one form of apparatus suitable for carrying out the invention.

DETAILED DESCRIPTION OF THE INVENTION v The improved recovery process of the invention may lbe generally employed in the i separation of aromatic hydrocarbons from non-aromatic hydrocarbons, for example, naphthenic or aliphatic hydrocarbons. Preferably itis employed in the separation of gasoline boiling range aromatics from similar-boiling non-aromatics, that is, the separation of aromatics of from 6 to about 9 carbons from parains of from about 5 to about 9 carbons and naphthenes of from about 6 to about 9 carbons. Suitable feedl stocks also include narrower boiling hydrocarbon mixtures, such as, for example, mixtures of benzene, cyclohexane, heptanes, mixtures of toluene, methylcyclohexane, and octanes, or mixtures of xylenes, ethylbenzene, dimethylcyclhexane, ethylcyclohexane, and nonanes.

The parainic hydrocarbon which is added to the extractive stripper feed is liquid and preferably has an initial boiling point that is from about 20 C. to about C. higher than the end boiling point of the nonaromatics in the hydrocarbon feed mixture. Most preferably, the added liquid heavy hydrocarbon has an initial boiling point that is from about 30 C. to about 75 C. higher than the end boiling point of the non-aromatics in the hydrocarbon feed mixture. Branchedand straightchain parains maybe used.

In the separation of gasoline boiling range materials, parans of from about 11 to 20 carbon atoms are very suitableA as added heavy hydrocarbons.

A very suitable source of heavy paraiiins for use with gasoline boiling range hydrocarbons is an essentially aromatics-free paraffin kerosene or a gas oil boiling range mixture of paraflns. p v i Only minor amounts of heavy paraflinic hydrocarbon need be added to the stripper to obtain the benefit of the invention. Additions of from about 0.001 p.p.m. by weight to about p.p.m. by weight, based on the feed to the stripper, are suitable with amounts of from about 0.002 p.p.m. by weight to about 20 p.p.m. by weight being very suitable and amounts of from about 0.005 p.p.m. by weight to about 10 p.p.m. by weight being preferred.

Referring now :to the figure, an exemplary application of the invention is as follows. A mixed hydrocarbon stream, containing about 60% by weight of aromatic hydrocarlbons of from about 6 to about 8 carbons and about 40% by Weight of parafnic hydrocarbons of 6 to 9 carbons and naphthenic hydrocarbons from 6 to 9 carbons is introduced continuously into the bottom of the liquid/liquid extractor 11, herein shown as a rotating disc contactor, through line 12. Sulfolane (tetramethylene sulfone) is introduced into the top of extractor 11 through line 14. The two liquid streams are contacted in countercurrent. A rafnate low in aromatics is removed through line 15 to phase separator 16 where the rainate phase is separated from a small Sulfolane extract phase. The ratlinate phase is removed through line 17. A Sulfolane extract stream is removed from extractor 11 through line 19 to phase separator 20 where a Sulfolane extract phase is separated and removed through line 21. A small hydrocarbon phase is removed from phase separator 20 and either discarded through line 22 or returned to line 12 through line 24. The Sulfolane extract phase from separator 16 passes part recycled to line 14 Y hithrough line 25 to line'21. About three p.p.m. by weight respectively.

The following experiments illustrate the abilityy of heavy hydrocarbons to reduce foaming during separation of hydrocarbons from a sulfolanefaromatic extract.

. (I) .A platformate gasoline was extracted with Vsulfolane to produce an extract containing about 83% by weight sulfolane and about 17% by weight hydrocarbon which vwas madeup primarily ofharomatics with 6 to 9 carbon atomsbut also contained about parans with and/or 29through lines 3 6 or 37 amount of light parains, the lcovering the aromatics in Va Vhigh -state of purity froirrthe improvement comprising reresidual light paraffin-containing sulfolane extract by (a) subjecting the sulfolane extract to extractive stripping in the presence of from about 0.001 p.p.m. by weight to about 100 p.p.m. by weight of added 11 to 20carbon liquid parainic hydrocarbon to obtain a stripperoveheadconsisting essentiallyrof residual light paraflins and a ,stripper liquid bottoms comprising sulfolane, aromatics, and added paraflnic hydrocarbon, aud (b) fractionlly distilling the stripper liquid bottoms to obtain a distillate consisting essentially of aromatics and a secondfliquid bottoms consisting essentially 'of` sulfolane and added paraflinic hydrocarbon. 'r l 2. The process in accordance with clair'nl Vwhereinlthe added paraiiinic hydrocarbon is Vvadded in amount of from about 0.002 p.p.m. by weight to about p.p.m. by Weight. 3. The process in .accordance with claim Zwherein the L mixture of gasoline boiling rangehydrocarbonsto be sep- 5 to 9 carbon atoms and naphthenes with 6 to 9 carbon atoms. Thisextract was distilledin a glass sieve tray distillation column having` an internal diameter of 50 mm. The height of the liquid/vapor foam bed on the glass trays was measured to determine the foaming tendency of the extract. The height of the vapor` liquid foam bed on the glass trays was remeasured following the addition of 0.1 p.p.m. of heavy paralin. (hexadecane) and again following addition of 3 p.p.m. by weight of hexadecane. These additions reduced the foam height by 15 and 40% respectively.

(II) Experiment I was repeated, but the heavy parati-'1n this time was an odorless (paraffnic) kerosene, which was mainly parains of 12 to 17 carbon atoms. At a kerosene concentration of 0.01 p.p.m. by weight the reduction in foam bed height was 25%, at a concentration of 3 p.p.m. by weight the reduction was 40%.

We claim as our invention:

1. In the separation of aromatics from a mixture of gasoline boiling range hydrocarbons consisting essentially of parafns of from 5 to about 9 carbons, naphthenes of from 6 to 9 carbons and aromatics of from 6 to 9 carbons by selective liquid-liquid extraction with sulfolane to form an extract phase consisting essentially of sulfolane, 6 to 9 carbon aromatic hydrocarbons and a minor arated consists essentially of benzene, cyclohexane, and heptanes. Y

4. The process in accordance with claim 2 wherein the mixture of gasoline boiling range hydrocarbons tobevsop.- arated consists essentially ofk toluene, methylcyclohexanel, and octanes.

l5. The process in accordance with'claim 2 wherein the mixture of gasoline boiling range hydrocarbons to be separated consists essentially of xylenes, ethyl benzeneLldimethylcy'clohexane, ethyl cyclohexane, and nonanes.

Bozeman er n1. 208-321 HERBERT LEVINE, Primary Examiner i U.S. Cl. X.R. 

